The invention relates to a chuck for tool inserts.
A chuck for tool inserts, especially screw driver bits, of this genus is described in DE 3,829,331 A1. In this chuck, the tool insert used is forcibly held in place by means of a self-locking ball, where the ball is clamped between one of the six faces of the shaft of the tool insert which is inserted into the chuck and the tapering wall surface of a capping sleeve which is displaceable in the axial direction. To withdraw the tool insert which may be a bit, the ball must be released by displacement of the capping sleeve.
A disadvantage with chucks of this kind is the use of a ball which can be displaced and clamped in the chuck. This necessitates a costly construction for guiding the ball; furthermore, the functioning of the ball can be impaired by contaminants (e.g. foreign bodies) which find their way into the chuck.
In accordance with German Standard DIN 3126-C, it is known to provide tool inserts with a shaft having a hexagonal cross-section, with notches in the longitudinal edges of this hexagonal shaft; these notches form a snap-fit groove in the circumference of the shaft. The hexagonal shaft engages in the hexagonal cavity of a chuck, where a lock washer seated in the hexagonal cavity enters into this snap-fit groove. It is further known form DE 3,538,675 A1 to turn down the hexagonal shaft of the tool insert, from the working end as far as this snap-fit groove, so that the lock washer of the chuck engages ahead of the turned-down hexagonal shaft.
In these chucks, the tool insert is held in place by the spring action of the lock washer. A high spring force of the lock washer makes it difficult to change the tool insert, while a weak spring force results in an unreliable retention of the tool insert. In addition, metal fatigue which develops in the lock washer also makes unreliable the retention of the tool insert.
The object of the invention is to provide a chuck of the above-indicated type, which offers high operating reliability, is simple to manipulate and has a simple form of construction.